ZOOLOGY AND BOTANY^ MICROSCOPY, ETC. 219 



words, the branched mucous gland of Urochseta is traceable to the 

 specialized uephridial mass of the auterior segments of Perichseta, the 

 numerous external pores of the latter being replaced by the single 

 aperture of Urochseta. The ova are of larger size, and, like those of 

 Allurus, differ from those of most earthworms and agree with those of 

 the " Limicolfe " in this point. 



The alimentary canal of Dichogaster Damonis has two gizzards, each 

 of which occui^ies two segments, and in the characters of its nephridia 

 it approaches the " Limicolas." 



The latter part of the present memoir is taken up with further 

 remarks on the nephridia of earthworms. It seems possible to separate 

 into two groups the genera in which there is a greater or less develop- 

 ment of a network with numerous external pores in each segment, and of 

 these there appears to be a parallel series of differentiations. 



A. Nephridia forming a network, B. Nephridia forming a network 



consisting of excessively fine consisting of wider canals, 



canals, continuous from seg- discontinuous at the septa, 

 ment to segment. 



(1) ? (1) No further specialization. — 



Deinodrilus. 



(2) Nephridial network of pos- (2) Nephridial network partly 

 terior segments partly com- composed of tubes of greater 

 posed of tubules of greater calibre. Numerous coelomic 

 calibre. Numerous coelomic funnels. — Acanihodrilus multi- 

 funnels — Perichseta asjpergil- porus. 



lum. 



(3) Larger nephridial tubules in- (3) Nephridial network of pos- 



creased in size and forming a terior segments chiefly com- 

 nephridium nearly indepen- posed of larger tubules open- 

 dent of the finer tubes, and ing by a simple coelomic 

 opening by a single coelomic funnel. — Dichogaster. 

 funnel. — Perichseta armata, 

 Megascolides. 



In treating of the evolution of the nej)hridia the author states that, 

 in his opinion, the nearest approach to the primitive condition in the 

 Oligochfeta is to be seen in Perichseta aspergillum ; in the anterior 

 segments the resemblance to tlie Platyhelminth excretory system is 

 closest, for there is a continuous network of tubules with numerous 

 external pores. The network is not interrupted by the septa, and the 

 external pores are not in any way related to the segmentation of the 

 body. In the posterior segments the network of tubules are beginning 

 to break up into more or less isolated tufts, but this has no discernible 

 relation to the segmentation. From this point the modification of the 

 excretory system appears to have gone along one of two paths, but in 

 both cases the same goal — -the reduction of the nephridial system to a 

 pair of isolated nephridia in each segment — has been reached. Mr. 

 Beddard agrees with Prof. W^ B. Spencer that the single j)airs of 

 nephridia of certain earthworms (e. g. Perichseta Novse-Zealandise and 

 Perionyx) have arisen by a gradual increase in calibre of a part of the 

 nephridial network in each segment to form a pair of nephridia, and by 

 tlie gradual reduction of the rest. In certain other forms (e. g. AcantJio- 

 drilus Novse-Zealandise) tlie nephridia have been dei'ived through the 



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